The present invention relates to an improved electric cigar lighter or, more particularly, to an improved car-borne electric cigar lighter in which the electric circuit is closed by pushing and inserting a heater element into a spring contact so that the filament of the heater element is red-heated to facilitate lighting of a cigar or cigarette.
Most of automobiles are equipped with an electric cigar lighter built in the dashboard and the driver of the automobile can light his cigar or cigarette even during driving by using his single hand. The electric cigar lighter of this type is constructed from two parts including a heater element having a spiral filament and a spring contact which is electrically insulated from the car body and connected to the positive terminal of the car battery. When the heater element is pushed and inserted into the spring contact to be held therein, one of the terminals of the heater element is contacted with the spring contact while the other is in electrical contact with the car body connected to the negative terminal of the battery so as to close an electric circuit through which an electric current is passed to red-heat the spiral filament of the heater element.
FIG. 1 of the accompanying drawing shows an equivalent circuit of such a cigar lighter in which the switch 52 connected to the positive terminal of the battery and the switch 53 connected to the car body or the negative terminal of the battery are simultaneously closed by pushing and inserting the heater element with the filament 51 into the spring contact so that the filament 51 is red-heated to facilitate lighting of a cigar or cigarette.
FIG. 4 illustrates a perspective view of such a spring contact disassembled into parts. A spring receptacle 1 located just below the dashboard opening of a car has two vanes 1',1' made of a bimetal, between which the head of the heater element illustrated in FIG. 3 is inserted to be in contact therewith so that the electric circuit is closed. The bimetal vanes 1',1' are made usually from phosphor bronze having a thermal expansion coefficient of 18.times.10.sup.-8 cm/cm..degree.C. as the high-expansion metal and Invar or 42 Alloy having a thermal expansion coefficient of 1.2.times.10.sup.-6 cm/cm..degree.C. and 5.times.10.sup.-6 cm/cm..degree.C., respectively, as the low-expansion metal. When the temperature of the heater element is increased and reaches a certain elevated temperature, the bimetal vanes 1',1' are bent outwardly and lose contact with the heater element so as to open the circuit and prevent overheating. The spiral filament in the heater element is usually made of a resistance wire of an iron-chromium alloy having a volume resistivity of 1.2.times.10.sup.-4 ohm.cm and can be red-heated when an electric current of several amperes or 10 amperes at the largest is passed therethrough.
Following is a more detailed description of the structure of such a car-borne electric cigar lighter. It is usual that the electric cigar lighter of this type has a thermal fuse built in the spring contact as a safety means as is shown by the equivalent circuit illustrated in FIG. 2 having such a thermal fuse 9 which is melted down to open the electric circuit when the lighter is overheated. The structure of a conventional spring contact having such a thermal fuse is illustrated in FIG. 4 showing the spring contact disassembled into parts, in which the bimetal receptacle 1 is connected to a screw bolt 2 usually made from mild steel which penetrates the openings in an insulator 3 made from a ceramic, e.g., alumina, a connecting lug plate 4 having an opening of a larger diameter than the bolt 2, a mica-made insulating spacer 5, a connecting plate 4' and a spring washer 6 of mild steel and fastens them together by screwing a nut 7 thereto. The connecting lug plate 4 is electrically connected to the positive terminal of the car battery and the conduction between the connecting plates 4 and 4' is obtained through a thermal fuse 9 which at each end is inserted into and held by caulking at the caulking ears 8 and 8' on the connecting plates 4, 4', respectively, so as to ensure electric conduction to the bimetal receptacle 1.
When the head of the heater element 11, as shown in FIG. 3 is inserted into the bimetal receptacle 1 shown in FIG. 4 and contacted with the vanes 1',1', the electric current passes through the circuit of: the positive terminal of the battery, connecting lug plate 4, thermal fuse 9, connecting plate 4', spring washer 6 and nut 7, bolt 2, bimetal receptacle 1, spiral filament of the heater element and car body which in turn is connected to the negative terminal of the battery.
When the spiral filament of the heater element is heated in the above described manner to exceed a temperature of about 800.degree. to 900.degree. C. which is high enough for lighting of a cigar or cigarette, the bimetal vanes 1',1' are bent outwardly so as to automatically release the heater element from the receptacle and open the electric circuit. It is a rare but possible accident that the vanes 1',1' do not come off from contact with the head of the heater element even when the temperature is sufficiently high depending on the inserting condition of the heater element into the spring contact by any chance resulting in overheating. In such an accident of overheating, the heat of the heater element is conducted through the bolt 2, nut 7 and the like to the thermal fuse 9 which is then melted down to open the electric circuit and prevent further overheating resulting in a hazard of fire. In an ordinary operating condition, the thermal fuse 9, which is made from a wire of a low melting-point alloy of tin and lead having a melting point of 200.degree. to 300.degree. C. and has a sleeve of a thermo-plastic resin such as polyethylene, is thermally insulated from the heater element with the ceramic insulator 3 interposed therebetween so as to be prevented from untimely melting down.
The conventional car-borne electric cigar lighter of the above described type has disadvantages in several respects as a consequence of the use of a thermal fuse 9 as a safety means which connects the connecting plates 4,4' fastened together with an insulating mica spacer 5 interposed therebetween. Even by setting aside the disadvantage that a thermal fuse must be prepared separately for each lighter, the connecting plates 4,4' must be provided with the caulking ears 8,8', respectively, by means of which the thermal fuse 9 is mounted by caulking to bridge the connecting plates 4,4' after the other parts have been assembled together taking an additional labor in the line of the assemblage works.